Resurrecting my new XJ700X

This bike has sat for about a year, but before I even touched anything on it, I was able to fire it up with the choke on when it warmed up, choke was off, but you would have to give it a little bit of gas to keep it going or else it would die. Naturally, I decided to clean the carbs, which I performed today. I let the carb bodies soak overnight in that Gunk carb cleaner (the stuff that comes in the paint can) and I cleaned the rest of the parts in boiling lemon juice. End result: like-new carbs inside and out.

So, I reassembled everything with the notion that this bike would fire right up and run flawlessly. Wrong. The bike will start with the choke on and idle around 4,500 RPMs. When the engine is warm, I can gradually let the choke off and the RPMs will fall to around 2,500RPM and the bike will appear to be fine for about 10-15 seconds, but then it'll just bog down and die out of nowhere. I generally have a tough time getting the bike to fire up again once this happens, but when I do, the same things happens that I just previously described.

So, some things I have done and noticed:

Carbs and all internals are clean

Float levels weren't messed with, but they all sit between 22.15 - 22.60 mm (measured with a caliper from the bottom of the carb body to the top of the rounded part of the float. I'm not even sure what they're supposed to be set to, anyway)

Mixture screws are turned out 3 full turns (I've been reading that this may be too much, but I figured this was the factory setting)

Two of the four diaphrams are in less than perfect shape (I have two good, used ones on the way)

When the bike begins to bog down and die, I can see sparks arcing from the plastic part of the plug boot to the engine block. I have no idea what is causing this or how to even fix it.

I think the fuel petcock might be bad. It doesn't matter what position it is in, fuel will pour out all over the place. I disassembled it and cleaned up the internals, but that didn't help.

Any further thoughts? I'm going to pull the plugs and check them, although I have a feeling they will be black and sooty. Problem is, a standard 5/8" spark plug socket doesn't fit in the holes of the XJ700X engine, so I need to find the toolkit that came with this bike and pray there is a spark plug removal tool in there. I was also thinking of swapping fuel tanks with my 1982 XJ650 to see if the malfunctioning petcock is the problem. Would a bad petcock exhibit the above symptoms?

 

18mm socket fits them if I remember right. If you have arcing from the plug boots that needs to be addressed soon same with the fuel pouring out very dangerous combo right there. Where is the fuel coming from the petcock itself? or the carbs? Did you read through the old school carb cleaning by Rickcomatic?, and the bench sync thread on here?? They are a must read to getting the carbs tuned and the bike running optimum. You can try cleaning the plug caps thoroughly but if they are arcing outside the plastic they will probably need to be replaced. At the very least pull and clean them and check out the plugs. a 5/8" socket should fall right in the holes but won't fit the plugs if you can't get a 5/8 to slide at least over the ceramic part of the plug you have parts of the boot stuck in there. The idle adjustment hangs down between the two center carbs back it off to lower the idle but if the carbs aren't sync'd properly the bike won't run properly. You can buy a rebuild kit for the petcock or buy a new one all together if you like.

 

First off, when you say you let the "carb bodies" soak overnight, are you talking about the parts with the throttle plates, linkage, and mixture screws? If so, you may have done more damage than good. The throttle shaft seals (rubber parts that don't like carb cleaner) are inside there trying to seal the shafts and keep the air out of the carbs.

I found it was all but impossible to sync my X1 until I replaced those seals....I could sync the carbs, they would be fine, I would twist the throttle a couple times, and they were off again. They were even leaking some gas out the sides after a longer ride.
Bad part is you will need to break the rack apart ALL THE WAY to replace those little buggers. The butterflies are held in with tiny soft little screws that are rivetted on the back to keep them from vibrating out, and everything fits together like a glove.

BUT, your problem sounds much more severe than leaky throttle seals, so I wouldn't worry about them right now.

Spark plugs and caps>> arcing to the cover is not a good sign.

When I got X2 the PO had left the little "screw on caps" on the tops of the plugs. Needless to say, the caps weren't even all the way onto the plugs or making consistent contact.
I'd suggest pulling the spark plug caps off, and taking a close look for cracks. Take the "guts" out of the inside and clean the corrosion. Cut a small bit of wire off and re-connect them so you get a "fresh bite" on some clean wire with the caps.
Pull the plugs. You'll need a 18mm deepwell socket, 3/8" drive craftsman fits down in that well just fine.
I'd put in some new plugs and make sure the caps snap on ALL THE WAY.

Then give it a try.
MOST likely you'll need to go back to the carbs. Enrichment circuit all clean? Emulsion tubes spotless? all the jets clean? "beany screens" clean? Float levels set properly? Check for full fuel flow on Prime? Is there an in-line fuel filter? Is this the OLD gas from last time you ran it? Check the air-box for our favorite mice hitch-hikers?

 

Oh...didn't even notice the leaking petcock.
You need to fix that first before you make a fireball toasted X.

That was another problem with X2 when I got her....petcock assembled wrong. No wonder the PO couldn't get her to run.

 

The mixture screws were removed, but the throttle plates and linkages were all still attached. I was under the impression that the only seal on there was a plastic seal of some sort that wouldn't be bothered by any carb/parts cleaner?

The plugs are brand new and don't have those "screw on caps", but I only see this arcing when the bike is bogging down and about to die. Otherwise, everything seems fine. I checked for cuts and cracks in in the boots, but they look great. I'll have another look.

The enrichment circuit is spotless. I blew carb cleaner through it and then used compressed air to blow it all out. Emulsion tubes and jets look brand new after I soaked them in boiling lemon juice. Screens look good, too.

Like I said in the original post, the float levels are set so that they are all within 1 mm of each other, but I don't know if they're set to spec. Do you happen to know the correct setting for them when the float bowls are off and the carbs are turned upside down? I know my '82 XJ650 had a spec of 17.5mm +/- 1mm from the float bowl mounting surface on the bottom of the carb to the top of the float. I can't seem to find anything on the Mikuni carbs.

There is no in-line fuel filter, but will be soon. The old gas was drained and new gas was put in. The airbox is clean, but I don't currently have it hooked up to the carbs. Just trying to get the thing to run and idle correctly before I destroy my hands putting those rubber boots on.

Also, there is full fuel flow on prime, as well as ON and RES because the petcock isn't working correctly. It doesn't need vacuum for the fuel to flow...it just flows. I'm going to swap tanks with my XJ650 to see if that helps cure the problem. I know for a fact that the petcock on my XJ650 is in good working order.

 

Okay, I just got back from some very limited testing as it's getting late and the smell of gasoline is making me feel lightheaded. I swapped tanks from my XJ650 (with working petcock) to the XJ700X to no avail. It started for a bit with choke fully on, but then gradually died out and I couldn't get the thing to start back up at all. Pulled the plugs expecting them to be completely black and soaked with fuel, but they were dry and they actually looked pretty decent. Cylinders 1 and 3 looked good, but cylinders 2 and 4 were rich. I also noticed that all of the plugs were gapped WAY too small, so I gapped them all to .032.

Still couldn't get the bike to fire. I don't think the working petcock is giving the bike any fuel, but I'll mess around with it some more tomorrow.

Oh, and where the heck do the two vacuum hoses go that come from the plastic T's between the carbs 1 and 2 and carbs 3 and 4? Are those just overflow hoses or do they actually go somewhere specific?

 

The service manual on the XJCD says 17.5 +/- 1.0mm, but mine were nowhere near that range. I ended up not using that method.

Book says 2.5 - 3.0 to start. I forget where I put mine at.

Mine does to a lesser degree; I tried replacing the guts, but it still didn't help. The problem is illustrated here.

Perhaps if the float levels were set too high and letting fuel leak by, but that's iffy.

Neg, Star Commander; NEG. There are two throttle shaft seals per carb body. On the Hitachis, they're not too difficult to get to (I've documented the procedure) but from what I'm told, on the Mikunis, getting the screws out from the butterfly plates can be extremely difficult, as the back of the screws have been peened/staked over. This requires that the back of the screws be ground off so they don't rip the hell out of the threads.

I didn't break the rack on the Mikunis, so I can't say exactly how this is done. Chacal would be more than happy to tell you, but just be warned he has an unhealthy dislike for Mikuni carbs.

The book also says that the fuel level should be measured at 3.0mm below the edge of the float bowl when it's mounted on the carb body. Since the Miks have "innies" instead of "outies" like the Hitachis do when it comes to float bowl drain ports, I'm sure you know that these carb prefer a different tool to measure the float level... which is illustrated here.

That is correct; so far I have been content to use the one that comes in the toolkit found under the seat. Thing is, with the plugs being recessed down in the head like they are (the idjits at Toyota did the same thing on my Tercel) it's necessary in this case, if using an aftermarket socket, to use a thin-walled model. And of course, this page goes into excruciating detail.

Aaaaaaaaand, this is where I insert the shameless plug; I know you've already had your carbs apart, but the instruction file on the XJCD for this purpose was lacking pictures, and indeed had asked for them. I provided them. You're probably thinking it might be a good idea to flush the coolant, and how does one do that? I did that too.

 

Thanks for the detailed reply! The link you provided for the carb cleaning is the same one that I used. That procedure didn't remove the butterflies or the shafts and it says to let the carbs soak overnight, so I figured anything on those shafts wouldn't be harmed. Well, looks like I have some more painstaking disassembly to do.

Also, thanks for the links to the Maxim-X site. I didn't even know that existed, but I've been doing a lot of reading there about potential problems with the bike.

I guess my first step to getting this thing working again is ordering an XJCD for my own personal reference as well as getting a new petcock. I'll probably wind up just getting a new one and being done with it as I've heard about fitment issues with rebuild kits.

I also have a friend with a rack of four Mikuni carbs from a Yamaha (he doesn't remember what model or year) that he's giving me. I figure they will at least be good for the hardware.

Again, does anyone know where the two vacuum lines coming off of the plastic T's go to? Mine are just hanging under the bike at the moment acting a as a vent/overflow.

 

If you submerged the entire body, then yes. I believe the original cleaning article said not to do so because of the throttle shaft seals. And speaking of which...

------------

THROTTLE SHAFT SEALS:


aaa) OEM and aftermarket Mikuni carb Throttle Shaft V-Seal (sometimes called an "O-Ring", but it's not!)...these are the seals on the outside of the carb body that the throttle shaft passes through. Uses 2 per carb, BUT......without taking the carbs apart from the rack, the only ones you can replace are the outer seals on the #1 and the #4 carbs. Unlike the QR-series "o-rings" that many people recommend using---AND WHICH DO NOT FIT PROPERLY---these "V-Seals" do have the correct O.D., I.D., and thickness to fit both the throttle shaft and the carb shaft seal bore recess correctly. Used on all XJ550, XJ650 Turbo, XJ700-X, XJ750-X, XJ900RK, and XJ1100 models.

HCP6838B OEM Mikuni throttle shaft V-seal, single:
$ 5.00

HCP6838BSET2 OEM Mikuni throttle shaft V-seal, pair:
$ 9.00

HCP6838BSET8 OEM Mikuni throttle shaft V-seal, set of 8:
$ 34.00


HCP38B Aftermarket Mikuni throttle shaft V-seal, single:
$ 3.75

HCP38BSET2 Aftermarket Mikuni throttle shaft V-seal, pair:
$ 7.00

HCP38BSET8 Aftermarket Mikuni throttle shaft V-seal, set of 8:
$ 25.00

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You can get ahold of the guy (HAP) who runs the site either by email, or I believe he inhabits the XJ mailing list.

Aye. The kit I got from Chacal didn't work as well as I'd hoped. I ended up putting the original diaphragm/D-ring back in; it worked for a little bit, but still drips.

Chacal does stock the petcocks, though. He also stocks the inline shutoff valve, which Rick seems to like, just in case.

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HCP628 OEM Complete Fuel Petcock. The vacuum port nipple points directly out towards the back of the bike (rather than being angled as the original) and the fuel inlet port nipple is tilted upwards at about a 45-degree angle and is NOT angled towards the center of the bike (as original), nor is the fuel inlet nipple as long as on an original petcock. Surprisingly, besides these minor differences, these petcocks look exactly the originals. Also, the changed inlet pipe orientation results in being able to install the rear petcock-to-tank mounting screw easily---on original petcocks, you basically have to almost hacksaw the screw off to remove/replace it or the fiber sealing washer! (a wonderful feat of factory engineering!). Includes the in-tank filter and the petcock-to-tank sealing o-ring. Fits all XJ700 and XJ900RK models. NOTE: petcock mounting screws and their washers are NOT included!
$ 91.00

HCPUPRB4 OEM used original Rebuilt Petcock. For XJ700 and XJ900RK models.
$ 59.95 + $ 15.00 refundable core charge.

rp3) Aftermarket Mini In-Line Fuel On-Off Valve. This 1/4" inlet/outlet fuel shutoff valve provides a fail-safe solution for leaky petcocks. Small size allows it to easily fit under the gas tank, within the petcock-to-carb fuel line. Lever handle can be set to full on or full off position. Best solution is to repair or replace a leaky petcock, but for a quick and easy solution, this valve will do the job.

HCP764 Mini In-line Fuel On-Off Valve:
$ 14.00

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As are mine.

 

A little update. I swapped tanks again with my XJ650. The bike still exhibits the same symptoms. Eventually fires with the choke on, revs shoot to 4500RPM, and if I gradually turn the choke off, the bike will sometimes stay idling at 2200RPMs, but then it just randomly decides it has had enough and dies. Most of the time if I turn the choke off, it'll just bog down instantly and die. Definitely exhibiting some strange symptoms, which has made it hard for me to pinpoint the problem.

But, I went over to my buddy's place and he had a full set of these same carbs in his garage. He wanted to use two of them for a project he is working on, so he let me have the other two free of charge. They're not in great shape, but I should be able to salvage some parts off of them. It'll be especially nice to have some extra diaphrams lying around (assuming they are good, knock on wood!).

Looks like throttle shaft seals will be on my next Chacal order (I've got two used diaphrams coming from him). I still feel like my problem is much bigger than throttle shaft seals, however. I tried to see if they are leaking by spraying propane all around them while the bike was running, listening for a change in engine speed, but I came up with nothing. I also sprayed around the rubber intake runners from the engine to the carbs and still, nothing.

One thing I AM certain of, though. The bike is getting too much fuel. I sniffed the crankcase oil and it reeked of gasoline, so I emptied the oil and it came out like water, and there was about 3 - 3.5 quarts that came out. I replaced the oil with some fresh Castrol GTX and messed around with the bike some more. Even in screwing around for 5 minutes, the oil in the sightglass went from looking like oil, to looking like coffee.

I'm going to pull the carbs off again and inspect them to see if I can figure out what the heck is wrong.

 

Wombat The bike will NOT IDLE OR RUN PROPERLY WITHOUT THE AIRBOX INSTALLED!!!! You are just going to frustrate yourself. With the more air coming in it just won't work. Hook up the airbox and giver a go you can make all the necessary adjustments -the floats with the box hooked up. There is simply no way to get the mixture screws and idle set properly with the airbox unhooked. The sys needs the air restriction of the box to work properly. If your carbs are not leaking gas from the shaft seals you may still be ok. Hook u pthe airbox and I would bet a dollars to donuts that you will find it much easier to get it tuned in.

 

Ha! I was kind of thinking to myself today, I should probably just hook the airbox up and see what happens, but I've run plenty of ATVs, as well as my XJ650, with the airbox disconnected and everything seemed to run smoothly. I'll hook up the airbox after lunch and cross my fingers that solves at least some of my problems.

Couple of sidenotes. While I had the thing idling with the choke on, I was playing with the diaphrams and the two air jets on the rear. I noticed if I placed my finger over the removable air jet and then removed it, the engine sped up, but it only did this on cylinders 1 and 4. Placing my finger over the removable air jet on cylinders 2 and 3 and then removing it had no affect on engine speed. These also are the two cylinders running rich, while the other two cylinders seem to be running about where they should. No idea if this means anything, but I thought I'd throw it in there.

I also found a little nipple that slid into the float bowl to check the float levels. I could only reach cylinders 1 and 4, but when I held up a clear tube along side of the carb and cracked the drain screw open, the gas would travel about 3/8 of an inch from the top of the float bowl. No idea what the level should be, but it seems fairly reasonable to me.

I'll definitely hook up the airbox and post my results. Crossing my fingers on this one.

 

Doublecheck to see if the jets/passages are open? Perhaps shoot some carb cleaner down the passages?

Um, that's way the hell low, dude. As I said before, the target level is 3 mm below the edge of the float bowl. To clarify, where the float bowl meets the gasket. 3/8 inch would be about 9.5mm.

Also, I typically set the float levels off the bike, where I can get to everything much easier.

 

I typically set them off the bike, too, but I use a set of calipers and measure from the bottom of the carb to the top of the float. However, like you said in a previous post, the 17.5mm +/- 1mm was nowhere near what they were set at.

I removed the carbs and checked all of the jets/passages. Everything looked to be in tip-top shape, but I sprayed some carb cleaner in there just for fun. I didn't touch the level of the floats just yet, mainly because they weren't tampered with when disaasembled the carbs the first time and they all seem to be within spec of each other. That'll do, for now.

I hooked the airbox up, installed a new filter, and screwed down the airbox top. I skeptically turned the bike over and it fired up, idling pretty high around 4500RPM. I thought to myself, great, that didn't fix anything, but I looked at the choke. It was off. A bit puzzled, I went to rev the motor. Revved smooth all the way to 10KRPM. Still puzzled, I revved it some more. Not a hint of hesitation. I let the bike warm up a bit only to find the idle sitting up at 4000RPM with the choke off. I messed with the adjustment screw, but it was ineffective. The natural idle of the bike stayed at 4000RPM. I decided to ride it around my field for a bit to celebrate my pseudo-victory.

Initial impressions: This bike is a whole different beast than my 650. It sounds different, handles different, and is much quicker. I hit 65MPH in no time, but figured it would be best to ease off a bit since I was riding in dirt. I had to feather the clutch in the turns because of the high idle, but after about 2 miles of riding, the idle seemed to drop down to 2500RPM (still high). There were a few times where I stopped the bike just to see if it would idle properly. It completely died on me once, like it was trying to find idle, but went too low (my idle adjustment screw might be backed out all the way, so that may be an issue).

So, I'm stuck now with a seemingly good running motor, but the idle is simply too high. Obvious problems are vacuum leaks, which I have been doing my best to try and find. I've been keeping an eye on the butterfly shafts and focusing the propane around there to see if the motor will speed up, but I haven't found anything. Another thought I had was the two vacuum diaphrams that I know are bad. Will the carb suck air through a leaking vacuum diaphram? The two diaphrams I have that are bad are because the previous owner didn't seat them properly in the groove before he screwed the carb cap on and it smashed them in a way that it ruined parts of the outside edge. I've been using them temporarily until I get my good, used ones from Chacal, but I wasn't sure if those not being 100% would affect the idle performance of the bike.

Another thing I've noticed, which may be another problem stemming from the vacuum diaphrams is that the engine speed does not decrease very uniformly in the mid range RPMs. If I'm cruising at 5KRPMs or so and let off the throttle, the engine kind of hangs there before dropping down to a lower speed. I'm thinking the diaphrams are not dropping as quick as they should. Does that sound plausible or am I completely off base?

Big thanks to schmuckaholic and 85MaximXX for getting me this far! Can't wait to start getting into the finer bits of tuning.

 

Quick update: Put several more miles on the bike tinkering and testing different things. The bike simply will not stay running at anything under 2000RPM. The idle is currently set to 2500RPM via the adjustment screw, but if I back it out any more, the bike falls below 2000RPM and sputters and dies. If I'm in motion and I let the clutch out and the RPMs fall below 2000RPM, I have to flutter the throttle to keep it running. If I'm cruising at 25MPH and in a gear high enough that the RPMs fall below 2000, I need to continually rev the bike to keep it running. Anything about 2000RPM, the bike screams and sounds great.

I'm crossing my fingers that my diaphrams get here by the end of the week to see if it cures my problem. I purposely put the bad diaphrams on the outside two carbs so swapping them out should be a breeze.

 

Glad to hear you at least got it to stay running. Another thing to check about the high idle is where the enrichment(choke) cable hooks up make sure the plungers are closing all the way. it kinda sounds like the pilot circuit is not allowing fuel thru but vacuum leaks can cause similar effects. what position are you running the petcock in? try it on PRI and see if you can then adjust down the idle. Maybe the vacuum line has some small leaks in it not allowing proper fuel flow at idle. The prime position doesn't need the vacuum supply to let fuel flow.

 

Good to hear you are making progress!

You've been messing with enough stuff that it probably needs a good carb sync at this point too. Although it probably doesn't pay until you get good diaphrams in those carbs.

The Mikuni carbs seem to be much more sensitive than the Hitachi. 1/8 of a turn on the sync screws will take it from a perfect purrrr to running on 2 cylinders the way it seems. I can't even seem to adjust the mixture screws without re-syncing the carbs.

Float levels are also very finicky IMO
I had one carb that was a little high. (maybe 2 mm high) I finally got it dialed in, and my mileage went from ~37 to ~44 mpg overnight.

If your airbox boots are a little hard, the $35 for a new flexible set will be the best investment in your sanity you can make (your hands will thank you too)

Make sure you have your "nipple caps" on the intakes and the vacuum line hooked up to the petcock (or cap that one too until you get your petcock fixed).
It will take a while, but once you get it dialed in you won't be able to wipe the grin off your face.

 

Wombat,

You might be complicating this a bit(a lot). No low Idle...pilot jet. Makes sure this passage is clear. My bike display the same symptom with no low idle under 2k. Fuel, fire, and air. The rest is fine tuning.

My bike sat for 18 yrs. Who knows what happened to the half tank of gas it had, but I know there were no adjustments and no modifications so everything was still the way they were so it was a matter of finding how clean I had to get everything before I even started to think about disassembling or replacing anything.

Put your mouth on it and blow. If air passes its clear or put a few drops of cleaner on it. If it goes down its clear. I tested most of the carb parts by putting my mouth on it and it responded well.

 

The petcock is in the "On" position, although it doesn't really matter where it's at since every position acts as "Prime." I will check the enrichment cable to make sure the plungers are fully closed when the choke is off.

The pilot jets were removed from the carbs, soaked in boiling lemon juice, and then I used carb cleaner to blow through the passageway, following it up by blowing an airhose through it. The end result, a very clean, almost brand-new looking pilot jet. It's possible that they've clogged again and, if swapping the diaphrams doesn't cure this problem, I'll remove the carbs and check those one more time.

My airbox boots are very flexible and easy to work with. I couldn't believe there was even LESS room between the carbs and the airbox than on my 650 - what a poor design. I will cap the vacuum line going to the petcock since it's basically useless at this point anyway. I think I will place another order with Chacal tonight for a new petcock and some other odds and ends.

It also seems my idle speed depends on the angle between the sun and the earth. I fired the bike up to take some video and it was idling at 2500RPM and holding. I fired it up 10 minutes later to take some more video, it wouldn't even start without the choke engaged. Once it did fire up, it wouldn't idle at all and I had to keep giving it gas, It just seems so erratic. This is the type of behavior I expect from a failing computer on a fuel injected bike, not from mechanically/vacuum controlled carbs. I'm stumped.

Video: http://videos.streetfire.net/video/1985 ... 179457.htm

In the video, you can hear it not even want to start up without a little bit of throttle and then it just doesn't want to idle at all. I have to flutter the throttle just to keep it going. It doesn't really seem to do this when I'm riding it, it just hovers at a high RPM, but when it's up on the center stand - like in the video - it just refuses to idle for me.

 

Wombat,

You might be complicating this a bit(a lot). No low Idle...pilot jet. Makes sure this passage is clear. My bike display the same symptom with no low idle under 2k. Fuel, fire, and air. The rest is fine tuning.

My bike sat for 18 yrs. Who knows what happened to the half tank of gas it had, but I know there were no adjustments and no modifications so everything was still the way they were so it was a matter of finding how clean I had to get everything before I even started to think about disassembling or replacing anything.

Put your mouth on it and blow. If air passes its clear or put a few drops of cleaner on it. If it goes down its clear. I tested most of the carb parts by putting my mouth on it and it responded well.

 

Just from reading other posts on here the gas that is in your oil is probably due to the leaking petcock. As far as the high idle goes, my X did that until I cleaned and bench synced the carbs with the instructions on this site. Now it idles like a dream and pulls hard up to redline. I also wonder where those tees between the carbs are supposed to hook up to, mine do not even have lines hooked up to them, but that could be because I am running pods.

 

I just noticed in a previous post that you gapped the plugs at .032. I am surprised no one else mentioned it, but the factory service manual says to gap them at .024-.028. This is also mentioned on the Maxim X site. Good luck and let us know how it goes

 

Wow, that low? Heh, maybe the plugs were gapped the right way before I put them to .032. I'll go back and change that next and see where that puts me.

 

You have to force yourself NOT to make "Fractional" adjustments to the Pilot Mixture Screws.
Once the Pilot Mixture Screws are in the near vicinity of providing a Mixture that will sustain Idle and supplement off-idle Mixture moving them more than a few degrees will place them in a position of being too Lean or too Rich.

The "Working distance" of the Pilot Mixture Screw is within 4-Degrees.
Finding the Initial Setting takes some patience, but once you know that you have a Pilot Mixture Screw close to where it needs to be for Fine-tuning ... you hardly need to move it very far to have the Mixture CHANGE quite a bit.

If you have Pilot Mixture Screws that are shouldered ... once the Shoulder is turned-out above the tiny O-ring ... you have the flow at Maximum -- weather you are at 3 Turns or the thing falling-out of the top.

You need to find the "Area" where you can adjust the amount of Air and the Fuel it drags along ... through the opening at the Carb Body and control that flow with minuscule adjustments to the Mixture Screw.

You might be running too Lean ... and turn the Screw less than a quarter-turn and go from being too Lean to too Rich because you've gone by the section in the bottom of the Screw that's cut to meter Fuel and air.

You have to finesse the Mixture by making microscopic movements to the Pilot Mixture Screw.
Giving-in to frustration and making an abrupt adjustment beyond a couple of degrees is just causing you to have tuning difficulty you wouldn't have if you move the Pilot Mixture Screws a hair at a time.

 

Good info, but I'm not even at that point yet. I'm still trying to figure out why the bike won't idle without dying. I haven't really messed with the mixture screws other than very small changes (like less than a quarter of a turn) to try and richen up two cylinders.

 

Tees between are for overflow. I have dropped the bike a few times in my day and wrecked it 3 times. I'm not bragging on me, I'm bragging on the bike.

I find it hard to believe that the bike is so sensitive. My bike ran great after the carbs were cleaned. When I went back over the bike I wondered what I was thinking all those years ago. My gap was way off and my 2nd and 3rd plugs were not completely tighten. I don't recall a lot except for suds and hits. I think I did not have the proper gap guage and figured it was close enough and I think I just forgot to tighten the plugs. It ran dispite my lameness. Make sure the carbs are clean. If there is a hole make sure it flows. If it goes up and down make sure it goes up and down.

Did I mention this bike still has its original plugs, air filter, and hasn't had a bath in over 18yrs? I did change the fluids.

Bottom line for me: make sure the carbs are clean. This bike is almost bullet proof.

 

Before I remove the carbs and disassemble them, I'm going to wait for my replacement diaphrams to come in. The ones I have now are visibly damaged, so no sense in trying to troubleshoot a bike with known faulty parts.

If the bike still doesn't want to run after that, I'm going to check the float levels and actually get a concrete measurement. If the floats are way off, I'm going to set them. While I have the carbs apart setting the floats, I'm going to triple check to make sure everything is clean. I've already been through the carbs twice and all was well, but I guess it won't hurt to triple check.

If at this point I'm still having issues, I'm going to be pissed, but at least I will have narrowed it down further.

 

The replacement diaphrams came in today and I swapped them in. The bike behaves a little differently. When it's cold, you'll need to choke it to get it to fire up, but once it's warmed up and the choke it off, it idles at a very steady 2000RPM. Seems to cruise around the same and accelerates quickly and smoothly - no complaints there. Still wants to bog under 2000RPM when I'm coasting in a tight turn and it'll want to hesitate when I give it a little bit of gas so it doesn't stall. The RPMs seem to fall a bit quicker than normal, but there is still a spot around 4500RPM where it gets hung up for a moment before it falls back to idle.

Next step - remove carbs, go through them again and make sure they are spotless and clear of debris, and adjust the float heights. I rechecked the float levels on 1 and 4 and they don't seem to be anywhere near each other (bike is on center stand on level ground).

Also ordered a new petcock and a front brake master cylinder. This bike is slowly making its way to the road. Unfortunately, the gas tank fell today and left a nice dent in the front so looks like I'll have some body work to do once I get this thing running perfect.

 

Carbs bench synced, pilot jets cleaned (they were fine), and floats set to the proper level (they were low as someone mentioned earlier in this thread). End result: a bike that still won't idle. I seem to have gotten rid of some of the low throttle hesitation, but it's definitely still present. As I coast to a stop, the bike will run down the RPM range and settle at 1000RPM for a moment, but then it'll gradually drop lower and lower until it stalls. If I try to revive it from stalling, it hesitates a lot and I have to give it some quick throttle pulses for it to come back to life.

I'm out of ideas for now. I'm going to do some searching on the forums for similar problems and possible solutions. I can tell you one thing, I am NOT remvoing the carbs again today. I need at least 24 hours rest from that.

 

pull your plugs and tell us what they look like if you can run the bike at 4500-5000 rpm for 15-20 seconds, Preferably if you can do this under load running down the road and hit the kill switch and shut the throttle off together and coast into your drive or place to work on the bike let it cool then remove them. You can do this stationary I personally don't like running a any motor at a high rpm without a load on it but thats just me. take some clear pics if you can and post the plugs You wnat a light tan color if they are white you need to richen things up, if they are dark you will need to lean it out a bit. Did you try to adjust the idle screw again now that you have the ather diaphrams in there?

 

I'd be willing to bet almost everyone has dropped a tank while working on their bike.
Do yourself a favor and make a "tuning tank" to use when you are tweaking the carbs and then you can put the tank safely on the floor ...where you can trip over it later (and scratch it)

The hanging idle is probably a small vacuum leak (possibly from the throttle shaft seals)

Keep at it. Getting these things dialed in after sitting for a while is NOT a 30 minute job.
Be careful though. Tweaking can become addictive!

If you can, polish the diaphram piston holes while you are in those carbs(search for Rick's post on that)
You want to pass the "clunk test" with flying colors. That will help give you great engine breaking when you close them down.

I believe Rick is also the counselor for "tweaking addicts anonymous"

 

Ugh, anyone know where I can pick up a cheap set of Mikuni BS33 carbs for cheap?

This has not been a good day.

 

If you have to "Blip-it" to keep from stalling ... you're probably too Lean.
But, if it's running half-way decently ... you're not too far off.

Begin by taking a peek at the Plugs and adding a couple of degrees of Richness to any of the Plugs that look clean.

 

This post is virtually a mirror image of what I am going through. Bike will not idle for more than a few seconds at 1100 rpm, then dies. If I bring up the idle, it goes to that rpm (2k or so) and stays there. I have a feeling I am running too lean, but cannot be sure. Other than that, the X runs like a scolded ape. I am learning a ton from this post, thanks guys.

 

And that's exactly what I thought. I also read a post on here by you that says the Mikuni's should be closer to 3 to 3-1/4 turns out. I had mine at 2 turns out, hence a lean condition. However, when I went to back out two of the mixture screws, they suddenly became stuck and wouldn't move anywhere. Now, I'm looking at two mixture screws with busted heads. I had my buddy try to extract them out, but that only ended in disaster, so I'm currently looking for a cheap set of Mikuni BS33 carbs to replace the two that I believe are now done for.

 

I think you just adjusted the hell out of them and lost the setting they were at. Its not easy finding the carbs. Good luck. I am sure you are not the only one who has gone thru this. I am sure there is plenty of good advice out there. I just passed 13k the other day.

Make sure the passage way for the pilots are clear clear too and if the is anything hanging out in the bowls it will definitely get drawn up in the jets. I ran wire thru that too.

 

Well, we need a set of carbs on one side, and it appears that I have my issue at least somewhat resolved. After my last post, I pulled all four of my plugs and they looked like white headed old men. All four were very lean. I believe that I had them set at 2.5 turns out, but may have been wrong. I came out on them something like 1.5 turns or somewhere there about. The bike now idles and only has a slight hesitation coming down from higher in the rpm range. I have a feeling a carb sync may do some good and as soon as the wx clears here, I will be doing that at my shop. I think I'll replace the plugs just for good measure, after all, I get them for something like $1 or so. Wombat, I'd find a machine/tool shop in your area. I broke off a stud in my case and they had that sucker out in no time. Cost me a whopping $23, well worth the time IMO.

 

Basically what needs to happen is the mixture screw holes need to be drilled out larger and retapped for a larger mixture screw that would also fit in the passageway. I'll just end up getting a spare rack.

 

I have always written a warning in most of my Post concerning the Pilot Mixture Screws softness and the absolute NEED for a PRECISION Fit of the Tool used to turn those Mixture Screws.

The warning I write is automatic because I know how easy they are to ruin.

You don't need new Carb Bodys.
You can Drill-out the Mixture Screws with ease.
The Mixture Screws are Brass or Bronze.

 

...and guess who sells them...

ims3) OEM Mikuni Idle Mixture Screw Set is correct for all original XJ550, XJ700-X, XJ750-X, and XJ900 carbs. Each complete set contains one brass slot-headed idle mixture adjustment Screw, the mixture screw Spring, the spring Washer, and the sealing O-Ring. NOTE: the tension spring contained in this kit is not correct for the XJ900RK models, but will work.

HCP3745 OEM Mikuni Idle Mixture Screw Set....contains the brass idle mixture screw, spring, spring washer, and the o-ring. Each:

$ 16.95

HCP3745SET4 OEM Mikuni Idle Mixture Screw Set, set of 4:

$ 64.95

 

Yea, it's a little more complicated than just getting new mixture screws. Believe me, I wish that were the case.

 

Just a thought, have you checked your coils? Maybe they are putting out a weak spark at idle/low RPM's. Just throwing it out there? Hope you get her straightened up soon.

 

Hey Wombat there are 2 sets of carbs for a maxim x on e-bay as we speak!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

shhhhhhhh!!!! 8)

 

good luck with them, looks like they'll go off at a low price...

 

Didn't get them. I didn't really want to pay any more than $100 for them considering the one carb body I need was JB welded back on. I guess someone needed them more than me

 

$100 is going to be a touch buy. You should just put the entire rack on when you get them instead of breaking the rack apart, then use the messed up ones for parts.

You wanted to know how my bike ran after the adjustment of the mixture screws. Well, she runs smoother, pulls better, runs cooler and other than hanging a touch (which I am going to attempt to correct today through a carb sync), she runs like a champ.

you might want to look in the classifieds for a guy in cali selling parts off his x. I got some parts off him, and I know he had a set of carbs for $75.

 

I wound up purchasing a different set that came off of a running bike that is being parted. I should hopefully receive them by the end of this week, but once I get them, they're coming apart, getting cleaned, bench synched, and floats will be set.

The price was significantly higher than the set on e-bay, but still not outrageous. I'm still well under $1000 on this bike, including the initial cost and parts so I'm not too upset. However, the bike still need a rear tire, which will be some $$.

In the meantime, I've been cleaning up the bike and even contemplated stripping the frame and repainting it. If I ever want to bring this bike back to excellent condition, the frame will need a repaint and I figure this would be the time to do it. Decisions, decisions...

 

wombat. I wouldn't paint the frame, I'd find a local powder coater and see what they can do for you. I completely stripped my bike this year, and altho the frame looks awesome, I spent 100 bucks on paint and prep. Guy up the street has an oven and he said he would do the frame and swingarm for $220. Man, if I had only found him sooner. BTW, that is a huge undertaking. It took me about 5 months to get mine back on the road after stripping her down. I'm getting all powder coated stuff in the future. I had my tins straightened and painted for $410 by an absolute pro. My father used him on his maxim x and he also did the paint on my dad's 57 t bird adn 57 nomad. I didn't mind paying what he charged, the paint alone cost $125!

 

I did some reading on painting the frame and that was enough for me to back off and say no. Once I get the X on the road, I think I may park the 650 and strip that down to the frame and completely restore it. It's in pretty rough shape, but I can't believe how well it runs.

In the time I've been waiting for the carbs to arrive, I've just been putting a little elbow grease into the frame and engine and trying to brighten it up a bit. It's looking better, but still needs a lot more work.